#ifdef __cplusplus
extern "C" {
#endif

#ifndef _CHECKSUM_H_
#define _CHECKSUM_H_


    /**
     *
     *  CALCULATE THE CHECKSUM
     *
     */

#define X25_INIT_CRC 0xffff
#define X25_VALIDATE_CRC 0xf0b8

#ifndef HAVE_CRC_ACCUMULATE
    /**
     * @brief Accumulate the X.25 CRC by adding one char at a time.
     *
     * The checksum function adds the hash of one char at a time to the
     * 16 bit checksum (uint16_t).
     *
     * @param data new char to hash
     * @param crcAccum the already accumulated checksum
     **/
    static inline void crc_accumulate(uint8_t data, uint16_t *crcAccum)
    {
        /*Accumulate one byte of data into the CRC*/
        uint8_t tmp;

        tmp = data ^ (uint8_t)(*crcAccum &0xff);
        tmp ^= (tmp<<4);
        *crcAccum = (*crcAccum>>8) ^ (tmp<<8) ^ (tmp <<3) ^ (tmp>>4);
    }
#endif

    /**
     * @brief Initiliaze the buffer for the X.25 CRC
     *
     * @param crcAccum the 16 bit X.25 CRC
     */
    static inline void crc_init(uint16_t* crcAccum)
    {
        *crcAccum = X25_INIT_CRC;
    }


    /**
     * @brief Calculates the X.25 checksum on a byte buffer
     *
     * @param  pBuffer buffer containing the byte array to hash
     * @param  length  length of the byte array
     * @return the checksum over the buffer bytes
     **/
    static inline uint16_t crc_calculate(const uint8_t* pBuffer, uint16_t length)
    {
        uint16_t crcTmp;
        crc_init(&crcTmp);
        while (length--)
        {
            crc_accumulate(*pBuffer++, &crcTmp);
        }
        return crcTmp;
    }

    /**
     * @brief Accumulate the X.25 CRC by adding an array of bytes
     *
     * The checksum function adds the hash of one char at a time to the
     * 16 bit checksum (uint16_t).
     *
     * @param data new bytes to hash
     * @param crcAccum the already accumulated checksum
     **/
    static inline void crc_accumulate_buffer(uint16_t *crcAccum, const char *pBuffer, uint8_t length)
    {
        const uint8_t *p = (const uint8_t *)pBuffer;
        while (length--)
        {
            crc_accumulate(*p++, crcAccum);
        }
    }




#endif /* _CHECKSUM_H_ */

#ifdef __cplusplus
}
#endif
